Hantaviruses are NIH category A pathogens. New World hantaviruses cause hantavirus cardiopulmonary syndrome (HCPS), a disease case with fatality rates that approach 40% in both North and South America. Although first recognized in North America, HCPS is a much larger problem in South America where cumulative numbers of cases and deaths from HCPS in Chile, Argentina and Brazil far exceed those in the United States. In a population one-twentieth that of the US, more total cases (604) have been in reported in Chile than in the US (~500 cases), and more cases and deaths occur each year in Chile than in the US. Humans acquire Andes virus (ANDV), the etiologic agent of HCPS in Chile, from virus-infected rodents, but ANDV is the only hantavirus that may then be transmitted from person to person. In Chile, this results in household case clusters, particularly among sex partners. In this second competitive renewal, the first aim is to refine the study of index cases with HCPS and prospectively study their close household contacts to evaluate risk factors for person to person transmission. Risk factors will be assessed through a questionnaire and through testing saliva, gingival crevicular fluid, respiratory and genital secretions, blood and urine for the presence of ANDV by RT-PCR and by viral culture in RT-PCR positive samples. The second aim is to enhance ANDV isolation and characterization using deep sequencing to evaluate the spectrum of viral variants from patients and rodents and use complementary approaches to facilitate recovery of replication-competent virus. The first goal is to determine whether there are physiological and genetic bottlenecks influencing the selection of particular ANDV variants in transmission from rodents to humans and from human to human. The second is to identify tractable approaches that lead to more efficient virus propagation and facilitate virus characterization. The third aim is to establish anti-ANDV vaccine evaluation capacity by a) developing test sites and b) developing and validating a high throughput assay for measurement of neutralizing antibody. Test sites will be established in rural, high-risk areas where both seroprevalence and vaccine acceptability will be determined. Validation of the BSL-2 assay will include transfer of an assay developed by Doms and colleagues and comparison results from the more laborious BSL-3 focus reduction assay. RELEVANCE: Andes virus is a hantavirus that causes a serious disease that kills almost 40% of those who become infected. This research is designed to help us learn how the virus is transmitted, information that could be used for education and prevention. The research will also develop test sites where a vaccine to prevent Andes virus infection could be tested and a blood test to see whether people respond to vaccination.